1. Field of the Invention
The present invention relates to a magneto-optical recording method for performing recording or erasure of information upon radiation of a light beam on a magneto-optical recording medium, and a magneto-optical recording medium used in this method.
2. Description of the Related Art
A magneto-optical recording technique for recording, reproducing, or erasing information upon radiation of a laser beam on a magneto-optical recording medium has been used in practical applications and is the most promising technique as a memory technique having both features of an optical recording technique (e.g., high-density recording characteristics and compatibility among recording media) and data rewritability of a magnetic recording technique. According to an existing practical magneto-optical recording method, a laser pulse beam modulated with data is focused and radiated on a recording layer, a coercive force of the heated portion is decreased below an externally applied magnetic field, and a direction of a magnetization of this area is changed to the direction of the externally applied magnetic field, thereby recording data. In order to rewrite data, a magnetic field is externally applied to the recording layer in a direction opposite to that in the recording mode to irradiate the recording layer with a continuous laser beam, thereby erasing the data. Thereafter, new data is written in the recording layer upon radiating laser pulse modulated corresponding new data. A disk memory requires two revolutions and switching the magnetic field at the time of data rewriting. As compared with a magnetic disk memory operated at the same speed, a rewriting speed is undesirably decreased less than 1/2, thus resulting in an essential drawback.
In recent years, various types of so-called overwriting methods for updating data in magneto-optical recording by one revolution as in magnetic recording are proposed. These conventional overwrite techniques are classified into a magnetic field modulation scheme and a light power modulation scheme.
The former scheme is to modulate an external magnetic field at high speed and to overwrite data in the same manner as in magnetic recording, as disclosed in Jap. J. Appl, Phys. Vol. 26, Suppl. 26-4, PP. 149-154, 1987 and IEEE Trans. Magn., Vol. 24, No. 1, PP. 666-669, 1988. This technique, however, has disadvantages in that a disk obtained by adhering two substrates is difficult to use, and compatibility with commercially available rewritable optical disks is difficult to establish. In addition, it is difficult to simultaneously achieve low power consumption and high transfer rate.
The latter technique is to change a light intensity or irradiation duration to overwrite data, as disclosed in Published Japanese Unexamined Patent Application No. 62-175949 and Appl. Phys. Lett., Vol. 52, No. 18, PP. 1,537-1,539, 1988. In this technique, however, control is complicated, and a compact apparatus is difficult to obtain. A satisfactory system has not yet been proposed.